1. Field of the Invention
The present invention relates to a current detection device, and in particular, to a current detection device having a magnetic sensor built into a choke coil.
2. Related Art
A current control device generally feeds back a detection signal obtained from a detection circuit to a control circuit for the sake of stabilization by means of a detection circuit having a sensing resistor for detecting a current or voltage connected in series with a load on an output side thereof in order to exert constant voltage and constant current control. This method has significant power attenuation because a current is constantly passed to the sensing resistor, which causes a serious problem to a power circuit for passing a high current, such as a resistance change due to heat generation of the sensing resistor.
As means for solving this problem, there is a current detection device conventionally known, which is provided with a choke coil for smoothing an input current or an output current and a magnetic sensor such as a Hall element as current detection means inside the choke coil.
FIG. 1 is a general current control circuit diagram which uses a current detection device having a magnetic sensor built into a choke coil. In FIG. 1, reference numeral 1 denotes a current detection device having a magnetic sensor 1a built into a choke coil, 2 denotes a switching element, 3 denotes a control circuit, and 4 denotes a load such as a motor. Thus, the current detection device 1 having the magnetic sensor 1a built into the choke coil detects a magnetic flux generated by the current passing through the choke coil with the magnetic sensor 1a, and performs a voltage amplification process and the like to output a signal voltage proportional to the current to the control circuit.
Circuit configuration of the current control circuit is widely known, and so a detailed description of the circuit will be omitted. As for the magnetic sensor 1a, it uses a Hall IC having a Hall element, a voltage amplifier circuit and the like built therein.
FIG. 4 is a sectional view of the current detection device 1. As shown in FIG. 4, the choke coil is composed of a choke core on which winding is performed. The choke coil is a closed magnetic circuit combining an E-shaped core 11 with an I-shaped core 12, where a wound coil 13 is implemented on a center magnetic leg 11a of the E-shaped core 11, and a gap 15 is provided between an end of the center magnetic leg 11a and the I-shaped core 12.
The gap 15 is intended to prevent the choke coil from losing its function as a choke coil as the coil 13 becomes saturated with a high current passing through it, rapidly decreasing inductance of the choke coil. The magnetic sensor 1a is placed in the gap 15 to detect a magnetic flux which penetrates between the center magnetic leg 11a and the I-shaped core 12 according to the current passing through the choke coil. It is thereby possible to obtain a control signal (refer to Patent Document 1).
[Patent Document 1] Japanese Patent Laid-Open No. 2002-181851
[Patent Document 1] Japanese Patent Laid-Open No. 2001-194392
As for the above current detection device, placement of the magnetic sensor and the core is important in order to accurately detect the magnetic flux according to the current passing through the choke coil with the magnetic sensor. Especially, it is an important problem, for the sake of improving detection accuracy of the current detection device, to place the magnetic sensor 1a in the gap 15 between the center magnetic leg 11a of the E-shaped core 11 and the I-shaped core 12.
The present invention has been made in view of the problem, and an object thereof is to provide a low-cost current detection device having the magnetic sensor easily placed on the choke coil for the purposes of reducing assembly and manufacturing costs and miniaturizing the product.